Mode-switching of audio amplifiers

ABSTRACT

In some embodiments, an audio amplifier can be controlled by a method that includes generating an enable signal based on a masking sound in an audio signal, and controlling a mode transition of the audio amplifier between a current source mode and a voltage source mode based on the enable signal. The mode transition of the audio amplifier can result in an artifact sound, the generating of the enable signal and the controlling of the mode transition can be achieved such that the artifact sound is substantially masked by the masking sound.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. application Ser. No.16/926,680 filed Jul. 11, 2020, entitled CIRCUITS, DEVICES AND METHODSRELATED TO MODE-SWITCHING OF AMPLIFIERS, which claims priority to U.S.Provisional Application Nos. 62/872,771 filed Jul. 11, 2019, entitledCIRCUITS, DEVICES AND METHODS RELATED TO MODE-SWITCHING OF AMPLIFIERS,and 62/881,448 filed Aug. 1, 2019, entitled CIRCUITS, DEVICES ANDMETHODS RELATED TO MODE-SWITCHING OF AMPLIFIERS, the benefits of thefiling dates of which are hereby claimed and the disclosures of whichare hereby expressly incorporated by reference herein in their entirety.

BACKGROUND Field

The present disclosure relates to mode-switching of amplifiersprocessing signals such as audio signals.

Description of the Related Art

In many audio applications, sound provided by a speaker results from anaudio signal being amplified by an amplifier, and the amplified audiosignal being provided to the speaker. When implemented in a portableaudio product having a limited power source such as a battery, operatingmode of such an amplifier can be changed to allow a longer operatingperiod with the limited power source.

SUMMARY

In some implementations, the present disclosure relates to an audiocontroller that includes a mode state engine configured to receive anenable signal and generate a control signal for controlling a modetransition of an amplifier between a current source mode and a voltagesource mode, with the mode transition of the amplifier resulting in anartifact sound. The audio controller further includes an enablecomponent configured to provide the enable signal to the mode stateengine based on a masking sound in an audio signal, such that theartifact sound is substantially masked by the masking sound during themode transition of the amplifier.

In some embodiments, the enable component can be configured such thatthe masking sound is selected to be spectrally similar to the artifactsound. The enable component can be configured such that the maskingsound is identified based on a comparison of a crest factor of the audiosignal and a crest factor threshold level. The crest factor of the audiosignal can include a high frequency crest factor. The enable componentcan include a comparator configured to generate an output based on acomparison of the high frequency crest factor and the crest factorthreshold level. The enable component can further include a high passfilter and an absolute value circuit, such that the audio signal passedthrough the high pass filter and the absolute value circuit provides thehigh frequency crest factor. The enable component can further include adelay component configured to provide a time delay for the output of thecomparator.

In some embodiments, the crest factor of the audio signal can beobtained by a combination of a peak audio level of the audio signal andan average audio level of the audio signal. The crest factor of theaudio signal can be obtained by a ratio of the peak audio level over theaverage audio level. The peak audio level and the average audio levelcan be obtained from a common frequency range. The common frequencyrange can include a frequency associated with the artifact sound. Thecommon frequency range can include a high frequency range.

In some embodiments, the peak audio level can be obtained from a firstfrequency range, and the average audio level can be obtained from asecond frequency range that is different than the first frequency range.The first frequency range can include a frequency associated with theartifact sound. The first frequency range can include a high frequencyrange. The second frequency range can include a frequency range outsideof the first frequency range. The second frequency range can include alow frequency range.

In some embodiments, the peak audio level can be obtained by passing theaudio signal through a peak level circuit that includes a high passfilter. The peak level circuit can further include an absolute valuecircuit implemented at an output of the high pass filter.

In some embodiments, the average audio level can be obtained by passingthe audio signal through an average level circuit that includes anabsolute value circuit. In some embodiments, the average level circuitcan further include a low pass filter implemented at an output of theabsolute value circuit. In some embodiments, the average level circuitdoes not include a high pass filter, and the average audio level can beobtained without any high pass filtering of the audio signal.

In some embodiments, the audio controller can further include a targetmode component configured to identify a target mode for the modetransition among a plurality of modes including the current source modeand the voltage source mode. The target mode component can be configuredsuch that the target mode is identified based on an average audio signallevel and threshold levels associated with the current source mode andthe voltage source mode. The threshold levels associated with thecurrent source mode and the voltage source mode can be different. Thethreshold level associated with the current source mode can be lowerthan the threshold level associated with the voltage source mode.

In some embodiments, the target mode component can include a comparatorconfigured to generate an output representative of the target mode basedon a comparison of the average audio signal level and a selected one ofthe threshold levels associated with the current source mode and thevoltage source mode. In some embodiments, the target mode component canbe configured such that the average audio signal level is obtained bypassing the audio signal through an absolute value circuit and a lowpass filter. In some embodiments, the average audio level can beobtained from a frequency range that is different than a frequency rangeassociated with the artifact sound. The frequency range associated withthe artifact sound can include a high frequency range.

In some embodiments, the target mode component can be configured suchthat the selected one of the threshold levels corresponds to a presentmode. The target mode can be the voltage source mode if the present modeis the current source mode, and the average audio signal level isgreater than the threshold level corresponding to the current sourcemode. The target mode can be the current source mode if the present modeis the voltage source mode, and the average audio signal level is lessthan the threshold level corresponding to the voltage source mode.

In some embodiments, the audio controller can further include a lowaudio component configured to identify a low audio condition thatprovides a reduced level of the artifact sound when the mode transitionoccurs during the low audio condition. The low audio condition caninclude a zero crossing condition.

In some embodiments, the mode state engine can be further configured tosupport a change in output resistance of the amplifier in one or moresteps. The change in output resistance of the amplifier can be in aplurality of steps. The plurality of steps in the change in outputresistance can be implemented by a plurality of respective comparatorseach generating a respective enable signal as an output based on a firstinput and a second input, with the first input including a peak audiolevel of the audio signal, and the second input including an averageaudio level of the audio signal mixed with a respective threshold value.

In some embodiments, a threshold value associated with an up changeinvolving an increase in the output resistance can be lower than acorresponding threshold value associated with a down change involving adecrease in the output resistance. The mode state engine can beconfigured to support the change in output resistance of the amplifierin a least number of steps without significantly impacting audibility ofthe artifact sound. The mode state engine can be configured generate anoutput signal to effectuate the change in output resistance based on theenable signals of the respective comparators. The output signal can becombined with a zero-crossing indicator signal, such that the change inoutput resistance is allowed to be effectuated during a zero-crossingevent.

In some embodiments, the mode state engine can be configured to enablethe change in output resistance in the plurality of steps or in a singlestep based on a relative strength of the masking sound. The change inoutput resistance can be implemented in the single step if the relativestrength of the masking sound is sufficiently high.

In accordance with a number of implementations, the present disclosurerelates to a method for controlling an audio amplifier. The methodincludes generating an enable signal based on a masking sound in anaudio signal. The method further includes controlling a mode transitionof the audio amplifier between a current source mode and a voltagesource mode based on the enable signal, with the mode transition of theaudio amplifier resulting in an artifact sound, and the generating ofthe enable signal and the controlling of the mode transition achievedsuch that the artifact sound is substantially masked by the maskingsound.

According to some implementations, the present disclosure relates to asemiconductor die that includes a substrate and an audio controllerimplemented on the substrate. The audio controller includes a mode stateengine configured to receive an enable signal and generate a controlsignal for controlling a mode transition of an amplifier between acurrent source mode and a voltage source mode, with the mode transitionof the amplifier resulting in an artifact sound. The audio controllerfurther includes an enable component configured to provide the enablesignal to the mode state engine based on a masking sound in an audiosignal, such that the artifact sound is substantially masked by themasking sound during the mode transition of the amplifier.

In some embodiments, the amplifier can be implemented on the substrate.

In some teachings, the present disclosure relates to a packaged modulethat includes a packaging substrate and an audio controller implementedon the packaging substrate. The audio controller includes a mode stateengine configured to receive an enable signal and generate a controlsignal for controlling a mode transition of an amplifier between acurrent source mode and a voltage source mode, with the mode transitionof the amplifier resulting in an artifact sound. The audio controllerfurther includes an enable component configured to provide the enablesignal to the mode state engine based on a masking sound in an audiosignal, such that the artifact sound is substantially masked by themasking sound during the mode transition of the amplifier.

In some embodiments, at least the audio controller can be implemented ona semiconductor die.

In a number of implementations, the present disclosure relates to anelectronic device that includes an amplifier configured to amplify anaudio signal, and an audio controller implemented to control theamplifier. The audio controller includes a mode state engine configuredto receive an enable signal and generate a control signal forcontrolling a mode transition of the amplifier between a current sourcemode and a voltage source mode, with the mode transition of theamplifier resulting in an artifact sound. The audio controller furtherincludes an enable component configured to provide the enable signal tothe mode state engine based on a masking sound in an audio signal, suchthat the artifact sound is substantially masked by the masking soundduring the mode transition of the amplifier.

In some embodiments, the electronic device can be a portable electronicdevice powered by a battery. In some embodiments, the portableelectronic device can be a wireless device.

In some embodiments, the electronic device can further include one ormore speakers in communication with the amplifier and configured togenerate sound waves based on the amplified audio signal. In someembodiments, the audio controller can be configured to support a modetransition of a respective amplifier associated with each of left andright audio channels at the same time for stereo operation ofcorresponding left and right speakers.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features of the inventions have been described herein. It isto be understood that not necessarily all such advantages may beachieved in accordance with any particular embodiment of the invention.Thus, the invention may be embodied or carried out in a manner thatachieves or optimizes one advantage or group of advantages as taughtherein without necessarily achieving other advantages as may be taughtor suggested herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a signal delivery configuration where an input signal isamplified by an amplifier to generate an amplified output signal.

FIG. 2 shows a more specific example of the signal deliveryconfiguration of FIG. 1, in the context of an audio application.

FIG. 3A shows signal traces of a 100 Hz tone before and after a gainchange for different gain reductions.

FIG. 3B shows Fast Fourier transforms of the signal traces of FIG. 3A.

FIG. 4A shows signal traces of a 100 Hz tone before and after a gainchange, resulting in various phase changes.

FIG. 4B shows Fast Fourier transforms of the signal traces of FIG. 4A.

FIG. 5 shows a plot of a glitch magnitude resulting from phasediscontinuity as a function of phase change.

FIG. 6 shows an example plot of glitch magnitude that may arise as atransient glitch.

FIG. 7 shows that in some embodiments, a mode-switching controller caninclude a mode state engine configured to receive a number of inputs andgenerate a control signal to effectuate a mode-switching operation undera desired condition.

FIG. 8 shows an example of how a target mode determination component ofFIG. 7 can be configured.

FIG. 9 shows an example of how a switch enable component of FIG. 7 canbe configured to identify a masking event.

FIG. 10A shows examples of various signals and states associated with anaudio signal.

FIG. 10B shows an expanded view of a portion of the example of FIG. 10A.

FIG. 11 shows an example of how a switch enable component of FIG. 7 canbe configured to identify a masking event based on peak and averagevalues that are based on different frequency components or ranges.

FIG. 12 shows that in some embodiments, an average audio level obtainedfrom an average level circuit of FIG. 11 can be utilized to determine atarget mode for a mode switching operation.

FIG. 13 shows an example of how a mode-switching operation involving aplurality of output impedance changing steps can provide a reduction ineffects of discontinuities.

FIG. 14 shows plots of gain errors and phase errors for a mode switchingoperation, for different numbers of steps of output resistance change.

FIG. 15A shows examples of various signals and states associated with anaudio signal.

FIG. 15B shows an expanded view of a portion of the example of FIG. 15A.

FIG. 16A shows a plot of glitch energy of step changes caused by phasemismatch, for the example audio signal and various traces of FIG. 15A.

FIG. 16B shows a plot where the glitch energy plot is divided by thecorresponding average audio level trace.

FIG. 17 shows that in some embodiments, a mode-switching controllerhaving one or more features as described herein can be implemented on asemiconductor die.

FIG. 18 shows that in some embodiments, a mode-switching controllerhaving one or more features as described herein can be implemented on asemiconductor die that also includes some or all of an amplifier forwhich mode-switching can be implemented as described herein.

FIG. 19 shows that in some embodiments, a mode-switching controllerhaving one or more features as described herein can be implemented on apackaged module.

FIG. 20 shows that in some embodiments, a mode-switching controllerhaving one or more features as described herein can be implemented onone or more semiconductor die, and such die can be mounted on thepackaging substrate of a module.

FIG. 21 shows that in some embodiments, an electronic device can includea mode-switching controller having one or more features as describedherein.

FIG. 22 shows a more specific example of the electronic device of FIG.21.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The headings provided herein, if any, are for convenience only and donot necessarily affect the scope or meaning of the claimed invention.

In many electronic devices such as portable audio products, it isdesirable to improve battery life to allow a longer operating periodbefore recharging or replacement of battery. A technique that can beemployed is to change the operating mode of an amplifier to, forexample, trade fidelity or noise floor for efficiency. For example, adesired performance characteristic of a portable audio device might beto have a high efficiency when program material is high level, but havea lower noise floor when the program material is low.

In many audio products, an issue of clicks or pops is typically known,and often can be problematic, especially if such noises occur duringaudio playback. Such noises can occur during mode switching operations,and are generally undesirable for a user.

Described herein are various examples related to techniques that allowminimization or reduction of likelihood of audible artifacts beingdetected by a user. As described herein, such techniques can includewhat could be considered masking of a noise associated with a modeswitching disturbance. In some applications, such a technique can beviewed as preserving signal-to-noise-ratio (SNR) of the sound presentedto the user during a mode switching disturbance.

FIG. 1 depicts a signal delivery configuration 110 where an input signalis amplified by an amplifier 102 to generate an amplified output signal.Such an amplified signal can be provided to a load 104. FIG. 1 furthershows that in some embodiments, a mode-switching controller 100 can beprovided to control switching between modes of the amplifier 102.Examples related to such control of mode-switching functionality aredescribed herein in greater detail.

FIG. 2 shows a more specific example of the signal deliveryconfiguration 110 of FIG. 1, in the context of an audio application.Other examples are described herein in the context of such an audioapplication. Accordingly, it will be understood that while variousexamples are described in the context of audio applications, one or morefeatures of the present disclosure can also be implemented in othertypes of signal delivery configurations, including non-audioapplications.

Referring to FIG. 2, a signal delivery configuration 110 can beimplemented where an input audio signal is amplified by an amplifier 102to generate an amplified output audio signal. Such an amplified audiosignal can be provided to one or more speakers (collectively indicatedas 104). FIG. 2 further shows that in some embodiments, a mode-switchingcontroller 100 can be provided to control switching between modes of theamplifier 102. In some embodiments, the amplifier 102 can be implementedas a single amplifier configured to operate in a current source mode(also referred to herein as a current mode or an I mode) or in a voltagesource mode (also referred to herein as a voltage mode or a V mode),first and second amplifiers configured to operate in current source andvoltage source modes, respectively, or some combination thereof.

It is noted that an amplifier operating in a current source mode resultsin a lower noise level; thus, such an operating mode is desirable at lowaudio levels. It is also noted that efficiency of the amplifieroperating in the current source mode is less efficient than a similaramplifier operating in a voltage source mode; thus, it is typicallydesirable to not always operate in the current source mode, in terms ofefficiency.

When switching between the current source mode and the voltage sourcemode, there can be one or more mode-switching issues that result inundesirable sound artifacts. For example, gain errors can arise during amode-switching process. In another example, phase errors can ariseduring a mode-switching process. In yet another example, switchingtransients can exist during a mode-switching process.

With respect to the gain errors, it is noted that in audio applications,a gain change involving an instantaneous or fast change in gaintypically results in a discontinuity proportional to the signal level ator near the instant of switching. Since such a discontinuity isproportional to the signal level, switching of gain at a low signallevel (e.g., relative to an average level) is better than switching ofgain at a high signal level. In such a context, switching at a zerocrossing of a signal is highly desirable and significantly reducesaudible transients during a gain change.

FIG. 3A shows signal traces of a 100 Hz tone before and after a gainchange soon after 2.73 sec. at one of a number of zero crossings, forgain reduction of 0.10 dB, 1.00 dB, 2.00 dB, 3.00 dB and 4.00 dB. FIG.3B shows Fast Fourier transforms of the signal traces of FIG. 3A. Asdiscussed above, little or no discontinuity arises if a mode switchingoccurs at a zero crossing, such as in the example of FIG. 3A. However,and as shown in the example of FIG. 3B, high-frequency spectral roll-offof about −40 dB/decade in gain step is present, thereby resulting inlikelihood of audible transients during or near the mode switchingoperation. In some situations, such audible transients can include, forexample, a noticeable timbre change.

FIG. 4A shows signal traces of a 100 Hz tone before and after a gainchange soon after 2.73 sec. at a zero crossing (for a signal notundergoing a gain change), resulting in phase changes of 0 degree, 1degree, 2 degrees, 4 degrees, 8 degrees and 16 degrees. FIG. 4B showsFast Fourier transforms of the signal traces of FIG. 4A. It is notedthat unlike the gain change example, discontinuity in phase arises evenif a mode switching occurs at a zero crossing. Further, and as shown inthe example of FIG. 4B, high-frequency spectral roll-off of about −20dB/decade in gain step is present, thereby resulting in higher potentialfor audible transients during or near the mode switching operation. Itis noted that in the example of FIGS. 4A and 4B, phase step disturbanceis hard to notice for the 1 degree change; but is readily noticeable forthe 4 degree (or higher) change.

As discussed above, a discontinuity in phase arises during a modeswitching operation even if the operation occurs at a zero crossing.FIG. 5 shows a plot of such a glitch magnitude resulting from the phasediscontinuity as a function of phase change in degrees.

FIG. 6 shows an example plot of glitch magnitude that may arise as atransient glitch. Such a transient glitch is not related to the signalbeing amplified, but is produced by other effects such as chargeinjection, resistor switching, and/or loop settling associated withoperation of the amplifier 102 of FIG. 2.

As described herein, a mode switching operation (e.g., between currentsource mode and voltage source mode) results in one or morediscontinuities due to signal components. Such discontinuities typicallyhave associated with them a significant amount of energy at frequencieswith large phase errors.

In some embodiments, a mode switching operation can be controlled byreducing the effects of the foregoing discontinuities, and/or by maskingan audible event associated with the discontinuities (whether or not theeffects are reduced). With the latter, a mode transition may be delayedfor a selected condition to provide the masking functionality. Examplesof such a selected condition are described herein in greater detail.

In some embodiments, an algorithm can be implemented to tune theforegoing selected condition based mode transition, so as to provide abalance between power usage efficiency and subjective audibility (ormasking effectiveness) of the masking functionality.

FIG. 7 shows that in some embodiments, a mode-switching controller 100(such as the mode-switching controller 100 of FIGS. 1 and 2) can includea mode state engine 120 configured to receive a number of inputs andgenerate a control signal to effectuate a mode-switching operation undera selected condition. For example, a low audio detection component 126can be implemented to provide an input signal to the mode state engine120 when an audio signal being amplified is at or near a zero crossing,or has a sufficiently low level. In some embodiments, such an inputsignal can be utilized to allow a mode-switching operation.

For example, a high logic signal provided by the low audio detectioncomponent 126 can correspond to the foregoing zero crossing orsufficiently low audio signal level and be utilized by itself or withone or more other conditions to allow a mode-switching operation. Insuch a configuration, a low logic signal provided by the low audiodetection component 126 can indicate that the audio signal is not at ornear a zero crossing, or has a high audio signal level. In someembodiments, such a low logic signal can be utilized to veto any otherenabled condition(s), so that a mode-switching operation does not occur.In some embodiments, a mode-switching operation can proceed despite alow logic signal provided by the low audio detection component 126, ifone or more selected conditions are satisfied.

In another example, and referring to FIG. 7, a target mode determinationcomponent 124 can be implemented to provide an input signal to the modestate engine 120. In some embodiments, such component can determinewhich mode the next transition should be. FIG. 8 shows an example of howthe target mode determination component 124 of FIG. 7 can be configured.In FIG. 8, a target mode determination component 124 can include acomparator 158 that compares an average audio signal level (e.g., seethe top panels in FIGS. 10A and 10B) with a threshold level (e.g.,threshold level T1, T2 or T3 in the top panels of FIGS. 10A and 10B).

By way of an example, the foregoing average audio signal level can beobtained by an audio level detector 150 configured to receive an audiosignal (e.g., a 48 KHz audio signal) and obtain an absolute value of theaudio signal with an absolute value circuit (ABS) 152. Such an absolutevalue signal can then be passed through a low pass filter (LPF) 154 toobtain the average audio signal level.

Also by way of an example, the foregoing threshold level can be based onthe present mode. In FIG. 8, such a present mode can be utilized to seta switch 156 to obtain and provide to the comparator 158 a thresholdvalue corresponding to the present mode. For example, if the presentmode is a current source mode, the switch 156 can be set to obtain andprovide to the comparator 158 a current source mode threshold value (T2in FIGS. 10A and 10B). Similarly, if the present mode is a voltagesource mode, the switch 156 can be set to obtain and provide to thecomparator 158 a voltage source mode threshold value (T1 in FIGS. 10Aand 10B).

With the foregoing inputs to the comparator 158, the following exampletarget mode determination can be implemented in some embodiments. If thepresent mode is a current source mode, and the average audio signallevel is greater than the current source mode threshold value (T2 inFIGS. 10A and 10B), the target mode can be set to be a voltage sourcemode; otherwise, the target mode can remain as the present mode. If thepresent mode is a voltage source mode, and the average audio signallevel is less than the voltage source mode threshold value (T1 in FIGS.10A and 10B), the target mode can be set to be a current source mode;otherwise, the target mode can remain as the present mode.

In some embodiments, the foregoing target mode can be utilized toeffectuate a masking event induced transition (from the present mode tothe target mode). If no attempt is made to transition based on a maskingevent, then a transition (from the present mode to the target mode) canbe made if the low audio component 126 is enabled (e.g., at the nextzero crossing), assuming that the target mode is different than thepresent mode.

In yet another example, and referring to FIG. 7, a switch enablecomponent 122 can be implemented to provide an input signal to the modestate engine 120 when a selected condition is detected. In someembodiments, such a selected condition can include a masking eventassociated with an audio signal being amplified. By way of non-limitingexamples, a masking event can include a sound (e.g., a snare drum sound,a guitar strumming sound, an onset of a phrase, etc.) that can mask, fora listening user, a sound artifact associated with a mode-switchingoperation.

In some embodiments, a masking event can be identified based on a crestfactor (CF) of an audio signal being amplified (e.g., a 48 KHz audiosignal). Such a crest factor can be calculated as a ratio of a peakvalue over an average value. FIG. 9 shows an example of how the switchenable component 122 of FIG. 7 can be configured to identify theforegoing masking event. In FIG. 9, a switch enable component 122 caninclude a first comparator 168 that compares a high frequency crestfactor of an audio signal with a crest factor threshold level (e.g., seethe second panels from the bottom in FIGS. 10A and 10B).

By way of an example, the foregoing high frequency crest factor can beobtained by passing an audio signal (e.g., a 48 KHz audio signal)through a high pass filter (HPF) 160, and then obtaining an absolutevalue of the high pass filtered signal with an absolute value circuit(ABS) 162. In the example of FIG. 9, such an absolute value of the highpass filtered signal is shown to be provided to one of the inputs of thefirst comparator 168.

Also by way of an example, the foregoing crest factor threshold levelcan be provided to another of the inputs of the first comparator 168, bymixing (at mixer 166) with a signal obtained from the foregoing absolutevalue of the high pass filtered signal (output of the ABS circuit 162)passed through a low pass filter 164. In FIG. 9, the first comparator168 is shown to provide an output based on the comparison of theabsolute value of the high pass filtered signal and the crest factorthreshold level. In some embodiments, such an output can be a high logicsignal if the absolute value of the high pass filtered signal is greaterthan the crest factor threshold level (thereby indicating a maskingevent), or a low logic signal otherwise.

In some embodiments, and as shown in the example of FIG. 9, the outputof the first comparator 168 can be time delayed by a hold time component170, and such a time delayed output logic signal can be provided to aninput of an AND gate 172. Another input of the AND gate 172 can beprovided with an output from a second comparator 176 that compares anabsolute value of an upconverted audio signal (e.g., a 3 MHz audiosignal obtained by converting the 48 KHz audio signal, passed through anabsolute value circuit (ABS) 174) with a maximum switching thresholdlevel. Thus, the AND gate 172 can output a switch enable signal based onthe AND logic operation of the delayed output of the first comparator168 and the output of the second comparator 176. Such a switch enablesignal can be high, indicating a presence of a masking event, or low,indicating absence of a masking event.

It is noted that many sounds that are spectrally similar to thediscontinuity-induced mode-switching sound (e.g., sound resulting fromphase error) have relatively high frequencies. Thus, the foregoingtechnique of identifying events with masking sounds (e.g., with highpass filtering of an audio signal) results in the masking sounds to bemore similar to the discontinuity-induced mode-switching sound.Accordingly, even if a discontinuity-induced mode-switching sound isaudible to a listener during a mode-switching operation, a masking soundpresent during the masking event-triggered mode-switch operationdesirably masks the perception of the audible discontinuity-inducedmode-switching sound.

In the example of FIG. 7, the mode-switching controller 100 can furtherinclude a hold-off timer 140 configured to support the delayfunctionality (170) described in reference to FIG. 9.

As discussed above, effects of discontinuities during a mode switchingoperation can be reduced. Performing a mode-switching operation at orclose to a zero crossing is an example of such a reduction. A reductionin effects of discontinuities can also be achieved by performing amode-switching operation in a plurality of output impedance (Rout)changing steps, instead of a single impedance change, between currentsource and voltage source modes. Such stepped impedance changes betweentwo values typically result in smaller phase errors than a singleimpedance change between the two values. Thus, in the example of FIG. 7,the mode-switching controller 100 can include a step period timer 142configured to support the foregoing stepped impedance changes.

In the example of FIG. 7, the mode-switching controller 100 can furtherinclude a component 130 configured to provide information about validmodes supported by the mode state engine 120. Such a component can beimplemented as, for example, a lookup table, memory, etc.

FIG. 10A shows examples of various signals and states associated with anaudio signal. FIG. 10B shows an expanded view of a portion of theexample of FIG. 10A. In FIGS. 10A and 10B, the bottom panel shows anormalized audio signal trace. The top panel shows a trace of theaverage audio signal level associated with the example normalized audiosignal trace (of the bottom panel), and various threshold levels (T1,T2, T3) discussed above in reference to FIG. 8. It is noted that T1corresponds to the voltage source mode threshold value, and such athreshold value can be, for example, 0.060 in the example normalizedscale of the average audio signal level. T2 corresponds to the currentsource mode threshold value, and such a threshold value can be, forexample, 0.040 in the normalized scale of the average audio signallevel. T3 corresponds to a low audio threshold value, and such athreshold value can be, for example, 0.010 in the normalized scale ofthe average audio signal level. In some embodiments, T3 can be utilizedto identify a low audio condition, including a zero crossing condition.

In FIGS. 10A and 10B, the second panel from the bottom shows a trace ofhigh pass crest factor levels (associated with the example normalizedaudio signal trace of the bottom panel), and a crest level thresholdlevel, discussed above in reference to FIG. 9. The second panel from thetop shows traces of mode states and target modes corresponding to theother traces, as described herein.

As described herein, a masking event can be identified and utilized tomask a sound associated with a mode switching operation. As alsodescribed herein, such a masking event can be based on comparison of acrest factor of an audio signal, with the crest factor being calculatedas, for example, a ratio of a peak value over an average valueassociated with the audio signal. In the example of FIGS. 9 and 10described above, both of peak and average values are obtained from asame pass filtered audio signal (e.g., high pass filtered audio signal),such that both of the peak and average values are based on similar passcomponent(s) or frequency range(s) of the audio signal (e.g., high passcomponents).

In some embodiments, it may be desirable to obtain peak and averagevalues that are based on different frequency components or ranges of anaudio signal. For example, a peak value can be based on a high passcomponent to identify sounds such as, for example, snare drum sound,guitar strumming sound, onset of a phrase, etc. that can mask, for alistening user, a sound artifact associated with a mode-switchingoperation. An average value, however, can be based on a frequency rangehaving a portion outside of a frequency range associated with the highpass component being utilized for the peak value. Such a frequency rangefor the average value determination may or may not include the frequencyrange associated with the high pass component.

For example, FIG. 11 shows an example of how the switch enable component122 of FIG. 7 can be configured to identify a masking event based on theforegoing peak and average values that are based on different frequencycomponents or ranges. In FIG. 11, an audio circuit 180 is shown toinclude a common input node 182 where a common audio signal (e.g., anaudio signal processed by an equalizer 181) is provided. From such acommon input node, a path 183 can be provided to an amplifier foramplification of the common audio signal. Also from the common inputnode 182, the common audio signal can be provided to an average levelcircuit 184 so as to allow determination of an average audio level. Alsofrom the common input node 182, the common audio signal can be providedto a separate peak level circuit 185 so as to allow determination of apeak audio level.

More particularly, and referring to FIG. 11, the peak level circuit 185can include a high pass filter 188 and an absolute value circuit (ABS)189 arranged in series. Accordingly, the common audio signal obtainedfrom the common input node 182 and passed through the peak level circuit185 results in a signal (Peak_HP) having a high pass component orfrequency range associated with a sound that is suitable as a maskingevent.

Also referring to FIG. 11, the average level circuit 184 can include anabsolute value circuit (ABS) 186 and a low pass filter 187 arranged inseries. Accordingly, the common audio signal obtained from the commoninput node 182 and passed through the average level circuit 184 resultsin an average audio signal having a frequency component or range that isdifferent than the frequency component or range associated with thePeak_HP signal. It is noted that in the foregoing example, the commonaudio signal from the common input node 182 is shown to be provided tothe ABS circuit 186 (of the average level circuit 184) without anyfiltering. In some embodiments, a shaping filter may be provided betweenthe common input node 182 and the ABS circuit 186.

In some embodiments, a crest factor can be obtained from the Peak_HPsignal and the average audio level of FIG. 11 (e.g., crestfactor=Peak_HP signal level divided by average audio level). In someembodiments, such determination and utilization of the crest factor canbe achieved by in a manner similar to the crest factor threshold and thecomparator 168 described herein in reference to FIG. 9.

It is noted that the example of FIG. 11 can be advantageous in audioapplications where audio material is dominantly low frequency. For suchaudio material applications, a crest factor that is more representativeof the frequency content can be obtained, and an artificially high crestfactor metric (even though high frequency masking energy was low) can beavoided.

FIG. 12 shows that in some embodiments, the average audio level obtainedfrom the average level circuit 184 of FIG. 11 can be utilized todetermine a target mode for a mode switching operation, similar to theexample of FIG. 8. In FIG. 12, a target mode determination component 190is shown to receive an average audio level information from an averagelevel circuit 184. In some embodiments, such an average level circuitcan be the average level circuit 184 of FIG. 11.

In the example of FIG. 12, the average audio level signal is shown to bepassed through another low pass filter 191 and provided to adetermination circuit 192. The determination circuit 192 is also shownto be provided with a current mode threshold value, a voltage modethreshold value, and a present mode information (Current/Voltage mode).Similar to the example of FIG. 8, the determination circuit 192 cangenerate a target mode as an output based on the foregoing inputs. Forexample, the determination circuit 192 in FIG. 12 can include acomparator and a switch similar to the comparator 158 and the switch 156of FIG. 8. In such a configuration, the average audio level from the lowpass filter 191 can be provided as one of the inputs of the comparator,and the current mode threshold value, the voltage mode threshold value,and the present mode information can be utilized by the switch toprovide an appropriate threshold value as the other input of thecomparator.

As described above, a mode-switching operation involving a plurality ofoutput impedance (Rout) changing steps can provide a reduction ineffects of discontinuities. FIG. 13 shows an example of how such Routchanging steps can be implemented.

Referring to FIG. 13, in some embodiments, a stepped Rout circuit 193can be implemented to allow a change in output impedance (Rout or Ro)associated with a mode switching operation, in one or more steps. Insome embodiments, it may be desirable to provide varying numbers ofsteps of change in output impedance during different mode switchingoperations. For example, if a mode switching operation involves, or islikely to involve, a relatively small error (e.g., phase error), such anoperation can be carried out with a one-step or a few-step impedancechange. In another example, if a mode switching operation involves, oris likely to involve, a relatively large error (e.g., phase error), suchan operation can be carried out with a larger number of steps ofimpedance change.

It is noted that in some embodiments, it may be desirable to skip aplurality of impedance change steps if a masking event is sufficientlystrong. In such a situation, the corresponding mode switching operationcan be achieved faster while benefitting from the masking effect.Accordingly, in some embodiments, the size of a masking event can drivesuch logic algorithm instead of the size of error associated with a modeswitching operation.

FIG. 13 shows that in some embodiments, the stepped Rout circuit 193 canbe configured to determine a number of steps of change in outputimpedance (Rout or Ro) during a mode switching operation, based on acrest factor (CF). For the purpose of description, it will be understoodthat such a crest factor can be obtained as in the example of FIG. 9, asin the example of FIG. 11, in another manner, or any combinationthereof.

For example, and assuming that the crest factor utilized for the steppedRout circuit 193 of FIG. 13 is obtained as described in reference toFIG. 11, one can see that a high pass peak level (Peak_HP obtained fromthe peak level circuit 185 of FIG. 11) and an average audio level(obtained from the average level circuit 184 of FIG. 11) can be providedto each of N comparators (194 a, 194 b, . . . , 194 c). Moreparticularly, the first comparator 194 a can be provided with the highpass peak level (Peak_HP) as one input, and the average audio levelmixed with a crest factor threshold level for 1-step impedance change(CF_Th_1step) as another input. If Peak_HP is greater than thecorresponding threshold value, the comparator 194 a can generate anoutput (1step_OK) indicating at least one step of impedance change isdesired.

Similarly, the second comparator 194 b can be provided with the highpass peak level (Peak_HP) as one input, and the average audio levelmixed with a crest factor threshold level for 2-step impedance change(CF_Th_2step) as another input. If Peak_HP is greater than thecorresponding threshold value, the comparator 194 b can generate anoutput (2step_OK) indicating at least two steps of impedance change isdesired.

Similarly, the N-th comparator 194 c can be provided with the high passpeak level (Peak_HP) as one input, and the average audio level mixedwith a crest factor threshold level for N-step impedance change(CF_Th_Nstep) as another input. If Peak_HP is greater than thecorresponding threshold value, the comparator 194 c can generate anoutput (Nstep_OK) indicating at least N steps of impedance change isdesired.

In the example of FIG. 13, the foregoing outputs of the comparators 194a, 194 b, . . . , 194 c can be provided to a control circuit 195. Such acontrol circuit can also be provided with a number of other inputs. Forexample, a minimum number of allowable or desired steps of impedancechange (Min_steps) and a maximum number of allowable or desired steps ofimpedance change (Max_steps) can be provided as inputs. Such minimum andmaximum numbers can be fixed values, programmable values, somecombination thereof, etc. In another example, a current outputresistance state (Ro_state) can also be provided as an input to thecontrol circuit 195.

In yet another example, a minimum step time (Min_step_time) can beprovided as an input to the control circuit 195. Such an input cancontrol timing and/or duration of the stepped changes in the outputresistance.

In yet another example, an exclusive-OR (XOR) of target mode(Mode_target) and present mode state (Mode_state) can be provided as aninput to the control circuit 195. In some embodiments, such an input canbe utilized to ensure that the stepped impedance change be implementedonly when the target mode is different than the present mode. Forexample, if the present mode is a voltage source mode (e.g.,Mode_state=1), and the target mode is also a voltage source mode (e.g.,Mode_target=1), then there is no need for a mode switch (and the XOR ofsuch two inputs is 0). In another example, if the present mode is avoltage source mode (e.g., Mode_state=1), and the target mode is acurrent source mode (e.g., Mode_target=0), then a mode switch canproceed (and the XOR of such two inputs is 1). It will be understoodthat similar logic can also be utilized if the present mode is a currentsource mode (e.g., Mode_state=0). It is noted that the foregoing featurecan allow saving of power by not performing mode switching when thepresent state and the target state are the same.

In the example of FIG. 13, the control circuit 195 can be configured togenerate a control signal Ro_target as an output based on some or all ofthe foregoing inputs. Such a control signal can include the number ofsteps to utilized in the output resistance during the corresponding modeswitching operation.

FIG. 13 shows that in some embodiments, the control signal Ro_targetoutput from the control circuit 195 can be combined with a zero-crossingsignal (ZX) by an enable mode switch circuit 196. Such a zero-crossingsignal (ZX) can be indicative of a zero-crossing condition (or near azero-crossing condition) detected by a zero-crossing detector 197. Insome embodiments, the enable mode switch circuit 196 can be configuredto allow implementation of the mode switching operation with the steppedoutput resistance change indicated by the control signal Ro_target. Inthe example of FIG. 13, the zero-crossing enabled mode switchingoperation is shown to be enabled by a zero-crossing enabled controlsignal Ro_state provided by the enable mode switch circuit 196. It isnoted that in some embodiments, the foregoing zero-crossing enablefeature may or may not be implemented.

In some embodiments, the control circuit 195 can be configured such thatthe control signal Ro_target is generated to enable an output resistancechange with the smallest number of step(s) (with the corresponding stepsize) acceptable among the various crest factor threshold levels(CF_Th_1step to CF_Th_Nstep) to provide efficiency in the correspondingmode switching operation without significantly impacting audibility ofthe mode switching sound. Such efficiency can include, for example, aquicker transition between the current and voltage source modes.

FIG. 14 shows plots of gain errors (upper panel) and phase errors (lowerpanel) for a mode switching operation, for different numbers of steps ofoutput resistance change. One can see that a large number of steps(e.g., N=4000) results in essentially no errors, and a no-step change(N=0) results in relatively large errors. One can also see that with arelatively small number of steps, including several steps such as N=4,errors can be reduced significantly when compared to the no-stepresistance change. With such a relatively small number of steps, errorscan be reduced while allowing the mode switching operation to beachieved in a relatively quick manner.

In some embodiments, when an output impedance (also referred to hereinas an output resistance) change is implemented in N steps during a modeswitching operation, a corresponding disturbance has a reducednormalized value that is roughly 1/N.

It is noted that in a voltage source mode, the corresponding outputresistance is approximately zero or very low. In contrast, in a currentsource mode, the corresponding output resistance is relatively high.Accordingly, a mode switching operation from a voltage source mode to acurrent source mode involves a resistance change from a low value to ahigh value. In contrast, a mode switching operation from a currentsource mode to a voltage source mode involves a resistance change from ahigh value to a low value.

In some embodiments, a resistance change from a low value (voltagesource mode) to a high value (current source mode) (also referred to asan up resistance change) can be substantially the same as, or bedifferent than, a resistance change from a high value (current sourcemode) to a low value (voltage source mode) (also referred to as a downresistance change). For example, the crest factor threshold levels(CF_Th_1step to CF_Th_Nstep in FIG. 13) for an up resistance change canall be the same, all be different, or partially the same and partiallydifferent, as/than a down resistance change. In the example of FIG. 13,inputs collectively indicated as 198 can be utilized to accommodate theforegoing crest factor threshold levels. Such threshold levels can beutilized as inputs to their respective comparators (194).

In some embodiments, a crest factor threshold for an up resistancechange (associated with a switch from a voltage source mode to a currentsource mode) can be selected to be lower than a corresponding crestfactor threshold for a down resistance change (associated with a switchfrom a current source mode to a voltage source mode). Such aconfiguration can improve efficiency of the corresponding mode switchingoperation, especially when implemented with the stepped resistancechange as described herein.

In some embodiments, the control circuit 195 of FIG. 13 can beimplemented as a part of the mode state engine 120 of FIG. 7, as aseparate control circuit, or some combination thereof. Similarly, eachof the related components such as the XOR gate, the zero-crossingdetector 197 and the enable mode switch circuit 196 can also be as apart of the mode state engine 120 of FIG. 7, as a separate controlcircuit, or some combination thereof.

FIG. 15A shows examples of various signals and states associated with anaudio signal. FIG. 15B shows an expanded view of a portion of theexample of FIG. 15A. In FIGS. 15A and 15B, the bottom panel shows anormalized audio signal trace. The top panel shows a trace of theaverage audio signal level and various threshold levels (T4, T5, T6)discussed above in reference to FIGS. 11-13. It is noted that T4corresponds to the voltage source mode threshold value, and such athreshold value can be, for example, 0.060. T5 corresponds to thecurrent source mode threshold value, and such a threshold value can be,for example, 0.040. T6 corresponds to a low audio threshold value, andsuch a threshold value can be, for example, 0.010. In some embodiments,T6 can be utilized to identify a low audio condition, including a zerocrossing condition.

In FIGS. 15A and 15B, the second panel from the bottom shows a trace ofhigh pass crest factor levels and a crest factor threshold level,discussed above in reference to FIGS. 11-13. The second panel from thetop shows traces of mode states and target modes corresponding to theother traces, as described herein.

FIG. 16A shows a plot of glitch energy of step changes caused by phasemismatch (which dominates the audible artifact), for the example audiosignal and various traces of FIG. 15A. FIG. 16B shows a plot where theglitch energy plot is divided by the corresponding average audio leveltrace. One can see that in either of the two plots of FIGS. 16A and 16B,the glitches are not audible.

In various examples described herein, sound levels such as average audiolevel and peak level are utilized by one or more features of the presentdisclosure, and related circuits such as absolute value circuits areconfigured to process such sound levels. It will be understood that oneor more features of the present disclosure can also be implementedutilizing other forms of representation of sound. For example, insteadof using an average level to determine a current source/voltage sourcetarget mode, similar determination can also be achieved using averageenergy. With such an example implementation, a square block can beutilized instead of an absolute value block.

In some embodiments, a mode-switching controller having one or morefeatures as described herein can be implemented in a number of products.For example, FIG. 17 shows that in some embodiments, a mode-switchingcontroller 100 having one or more features as described herein can beimplemented on a semiconductor die 200 having a substrate 202. In such aconfiguration, the mode state engine 120 of FIG. 7 can be implemented onthe substrate 202 of the die 200, and some or all of the variouscomponents can also be implemented on the same substrate.

FIG. 18 shows that in some embodiments, a mode-switching controller 100having one or more features as described herein can be implemented on asemiconductor die 210 having a substrate 212. Such a die can alsoinclude some or all of an amplifier 102 for which mode-switching can beimplemented as described herein.

FIG. 19 shows that in some embodiments, a mode-switching controller 100having one or more features as described herein can be implemented on apackaged module 300 having a packaging substrate 302. FIG. 20 shows thatin some embodiments, a mode-switching controller 100 having one or morefeatures as described herein can be implemented on one or moresemiconductor die 200, 210, and such die can be mounted on the packagingsubstrate 302.

FIG. 21 shows that in some embodiments, an electronic device 400 caninclude a mode-switching controller 100 having one or more features asdescribed herein. Such an electronic device can include an amplifier 404under the control of the mode-switching controller 100 as describedherein. Such an amplifier can receive a signal to be amplified from anaudio signal generator 402, and output an amplified audio signal to anaudio output device 406. In the example of FIG. 15, the electronicdevice 400 can also include a power source 408 configured to providepower to various components, including the amplifier 404.

FIG. 22 shows a more specific example of the electronic device 400 ofFIG. 21. In FIG. 22, a portable electronic device 400 can include amode-switching controller 100 having one or more features as describedherein. Such an electronic device can include an amplifier 404 under thecontrol of the mode-switching controller 100 as described herein. Suchan amplifier can receive a signal to be amplified from an audio signalgenerator 402, and output an amplified audio signal to one or morespeakers 406. In the example of FIG. 22, the electronic device 400 canalso include a power source implemented in the form of a battery 408;and such battery can provide power to various components, including theamplifier 404.

In some implementations, the portable electronic device 400 of FIG. 22can be, for example, a cellular phone, a smart-phone, a hand-heldwireless device with or without phone functionality, a wireless tablet,etc.

It is noted that an electronic device can include a plurality of audiochannels (with corresponding speakers) to provide, for example, stereofunctionality. In some embodiments, a mode-switching controller 100having one or more features as described herein can be configured tosupport switching of, for example, left and right audio channels at thesame time to minimize or reduce stereo stage balance issues.

The present disclosure describes various features, no single one ofwhich is solely responsible for the benefits described herein. It willbe understood that various features described herein may be combined,modified, or omitted, as would be apparent to one of ordinary skill.Other combinations and sub-combinations than those specificallydescribed herein will be apparent to one of ordinary skill, and areintended to form a part of this disclosure. Various methods aredescribed herein in connection with various flowchart steps and/orphases. It will be understood that in many cases, certain steps and/orphases may be combined together such that multiple steps and/or phasesshown in the flowcharts can be performed as a single step and/or phase.Also, certain steps and/or phases can be broken into additionalsub-components to be performed separately. In some instances, the orderof the steps and/or phases can be rearranged and certain steps and/orphases may be omitted entirely. Also, the methods described herein areto be understood to be open-ended, such that additional steps and/orphases to those shown and described herein can also be performed.

Some aspects of the systems and methods described herein canadvantageously be implemented using, for example, computer software,hardware, firmware, or any combination of computer software, hardware,and firmware. Computer software can comprise computer executable codestored in a computer readable medium (e.g., non-transitory computerreadable medium) that, when executed, performs the functions describedherein. In some embodiments, computer-executable code is executed by oneor more general purpose computer processors. A skilled artisan willappreciate, in light of this disclosure, that any feature or functionthat can be implemented using software to be executed on a generalpurpose computer can also be implemented using a different combinationof hardware, software, or firmware. For example, such a module can beimplemented completely in hardware using a combination of integratedcircuits. Alternatively or additionally, such a feature or function canbe implemented completely or partially using specialized computersdesigned to perform the particular functions described herein ratherthan by general purpose computers.

Multiple distributed computing devices can be substituted for any onecomputing device described herein. In such distributed embodiments, thefunctions of the one computing device are distributed (e.g., over anetwork) such that some functions are performed on each of thedistributed computing devices.

Some embodiments may be described with reference to equations,algorithms, and/or flowchart illustrations. These methods may beimplemented using computer program instructions executable on one ormore computers. These methods may also be implemented as computerprogram products either separately, or as a component of an apparatus orsystem. In this regard, each equation, algorithm, block, or step of aflowchart, and combinations thereof, may be implemented by hardware,firmware, and/or software including one or more computer programinstructions embodied in computer-readable program code logic. As willbe appreciated, any such computer program instructions may be loadedonto one or more computers, including without limitation a generalpurpose computer or special purpose computer, or other programmableprocessing apparatus to produce a machine, such that the computerprogram instructions which execute on the computer(s) or otherprogrammable processing device(s) implement the functions specified inthe equations, algorithms, and/or flowcharts. It will also be understoodthat each equation, algorithm, and/or block in flowchart illustrations,and combinations thereof, may be implemented by special purposehardware-based computer systems which perform the specified functions orsteps, or combinations of special purpose hardware and computer-readableprogram code logic means.

Furthermore, computer program instructions, such as embodied incomputer-readable program code logic, may also be stored in a computerreadable memory (e.g., a non-transitory computer readable medium) thatcan direct one or more computers or other programmable processingdevices to function in a particular manner, such that the instructionsstored in the computer-readable memory implement the function(s)specified in the block(s) of the flowchart(s). The computer programinstructions may also be loaded onto one or more computers or otherprogrammable computing devices to cause a series of operational steps tobe performed on the one or more computers or other programmablecomputing devices to produce a computer-implemented process such thatthe instructions which execute on the computer or other programmableprocessing apparatus provide steps for implementing the functionsspecified in the equation(s), algorithm(s), and/or block(s) of theflowchart(s).

Some or all of the methods and tasks described herein may be performedand fully automated by a computer system. The computer system may, insome cases, include multiple distinct computers or computing devices(e.g., physical servers, workstations, storage arrays, etc.) thatcommunicate and interoperate over a network to perform the describedfunctions. Each such computing device typically includes a processor (ormultiple processors) that executes program instructions or modulesstored in a memory or other non-transitory computer-readable storagemedium or device. The various functions disclosed herein may be embodiedin such program instructions, although some or all of the disclosedfunctions may alternatively be implemented in application-specificcircuitry (e.g., ASICs or FPGAs) of the computer system. Where thecomputer system includes multiple computing devices, these devices may,but need not, be co-located. The results of the disclosed methods andtasks may be persistently stored by transforming physical storagedevices, such as solid state memory chips and/or magnetic disks, into adifferent state.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The word “coupled”, as generally usedherein, refers to two or more elements that may be either directlyconnected, or connected by way of one or more intermediate elements.Additionally, the words “herein,” “above,” “below,” and words of similarimport, when used in this application, shall refer to this applicationas a whole and not to any particular portions of this application. Wherethe context permits, words in the above Detailed Description using thesingular or plural number may also include the plural or singular numberrespectively. The word “or” in reference to a list of two or more items,that word covers all of the following interpretations of the word: anyof the items in the list, all of the items in the list, and anycombination of the items in the list. The word “exemplary” is usedexclusively herein to mean “serving as an example, instance, orillustration.” Any implementation described herein as “exemplary” is notnecessarily to be construed as preferred or advantageous over otherimplementations.

The disclosure is not intended to be limited to the implementationsshown herein. Various modifications to the implementations described inthis disclosure may be readily apparent to those skilled in the art, andthe generic principles defined herein may be applied to otherimplementations without departing from the spirit or scope of thisdisclosure. The teachings of the invention provided herein can beapplied to other methods and systems, and are not limited to the methodsand systems described above, and elements and acts of the variousembodiments described above can be combined to provide furtherembodiments. Accordingly, the novel methods and systems described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the methods andsystems described herein may be made without departing from the spiritof the disclosure. The accompanying claims and their equivalents areintended to cover such forms or modifications as would fall within thescope and spirit of the disclosure.

1. A method for controlling an audio amplifier, the method comprising:generating an enable signal based on a masking sound in an audio signal;and controlling a mode transition of the audio amplifier between acurrent source mode and a voltage source mode based on the enablesignal, the mode transition of the audio amplifier resulting in anartifact sound, the generating of the enable signal and the controllingof the mode transition achieved such that the artifact sound issubstantially masked by the masking sound.
 2. The method of claim 1wherein the masking sound is selected to be spectrally similar to theartifact sound.
 3. The method of claim 1 further comprising generatingthe masking sound based on a comparison of a crest factor of the audiosignal and a crest factor threshold level.
 4. The method of claim 3wherein the crest factor of the audio signal includes a high frequencycrest factor.
 5. The method of claim 4 wherein the generating of themasking sound includes generating an output based on a comparison of thehigh frequency crest factor and the crest factor threshold level, suchthat the audio signal passed through a high pass filter and an absolutevalue circuit provides the high frequency crest factor.
 6. (canceled) 7.The method of claim 3 wherein the crest factor of the audio signal isobtained by a combining a peak audio level of the audio signal and anaverage audio level of the audio signal.
 8. (canceled)
 9. The method ofclaim 7 wherein the peak audio level and the average audio level areobtained from a common frequency range.
 10. The method of claim 9wherein the common frequency range includes a frequency associated withthe artifact sound.
 11. (canceled)
 12. The method of claim 7 wherein thepeak audio level is obtained from a first frequency range, and theaverage audio level is obtained from a second frequency range that isdifferent than the first frequency range.
 13. The method of claim 12wherein the first frequency range includes a frequency associated withthe artifact sound.
 14. (canceled)
 15. The method of claim 13 whereinthe second frequency range includes a frequency range outside of thefirst frequency range.
 16. The method of claim 15 wherein the secondfrequency range includes a low frequency range.
 17. The method of claim12 wherein the peak audio level is obtained by high pass-filtering theaudio signal.
 18. (canceled)
 19. The method of claim 12 wherein theaverage audio level is obtained by passing the audio signal through anabsolute value circuit.
 20. (canceled)
 21. (canceled)
 22. The method ofclaim 1 further comprising identifying a target mode for the modetransition among a plurality of modes including the current source modeand the voltage source mode.
 23. The method of claim 22 wherein thetarget mode is identified based on an average audio signal level andthreshold levels associated with the current source mode and the voltagesource mode.
 24. (canceled)
 25. (canceled)
 26. (canceled)
 27. (canceled)28. (canceled)
 29. (canceled)
 30. (canceled)
 31. (canceled) 32.(canceled)
 33. The method of claim 1 further comprising identifying alow audio condition that provides a reduced level of the artifact soundwhen the mode transition occurs during the low audio condition. 34.(canceled)
 35. The method of claim 1 further comprising implementing achange in output resistance of the amplifier in one or more steps. 36.(canceled)
 37. (canceled)
 38. (canceled)
 39. (canceled)
 40. (canceled)41. (canceled)
 42. (canceled)
 43. (canceled)
 44. A method for operatingan electronic device, the method comprising: operating an amplifier toamplify an audio signal; and controlling the amplifier, the controllingincluding generating an enable signal based on a masking sound in theaudio signal, the controlling of the amplifier further includingcontrolling a mode transition of the amplifier between a current sourcemode and a voltage source mode based on the enable signal, the modetransition of the amplifier resulting in an artifact sound, thegenerating of the enable signal and the controlling of the modetransition achieved such that the artifact sound is substantially maskedby the masking sound.
 45. The method of claim 44 wherein the electronicdevice is a portable electronic device powered by a battery. 46.(canceled)